De-gassing of liquids

ABSTRACT

A method of removing gases from a body of liquid, in which the gases have been dissolved at a first ambient pressure, comprising subjecting the liquid to a second ambient pressure of lower absolute value than the first ambient pressure, removing a proportion of the liquid from the body, causing the removed liquid to liberate at least some of the gases dissolved therein in the form of bubbles, and discharging the bubble-containing liquid into the remainder of the body in such a manner that the bubbles pass through the body, thereby releasing at least part of the gases dissolved therein.

United States Patent 1 Boucher et al. Mar. 27, 1973 1 DE-GASSING OF LIQUIDS [56] References Cited [75] Inventors: Harold T. C. Boucher, Thombury, UNITED STATES PATENTS near Bristol" Christopher Frank 3,590,559 7 1971 B tal ..261 124X Arthur h Whltchurch; 2,513,992 7/1950 133?? Martin West, Red1and,- all Of 1511- 2,901,031 8/1959 Powell et al. gland 3,446,488 5/ 1969 Mail et al 3,206,032 9/1965 Nottingham et al ..26l/124 x [73] Assignee: British Aircraft Corporation Limited, London, England Primary ExaminerReuben Friedman 22 Filed: Apr. 21 1971 Assistant Examinen-R. W. Burks Att0meySughrue, Rothwell, Mion, Zlnn & Macpeak [21] App]. No.: 136,023

. [57] ABSTRACT [30] Foreign Application Priority Data A method of removing gases from a body of liquid, in which the gases have been dissolved at a first ambient May 1, Great pressure, comprising subjecting the to a Second ambient pressure of lower absolute value than thevfirst [52] US. Cl. ..55/46, 55/ 199, 261/77, bi pressure, removing a proportion of the liquid 124 from the body, causing the removed liquid to liberate- [51] Int. Cl. ..B01d 19/00 'at least some of the gases dissolved therein in the form [58] Field of Search ..55/.44, 46, 53, 194, 196, 199, of bubbles, and discharging the bubble-containing liquid into the remainder of the body in such a manner that the bubbles pass through the body, thereby releasing at least part of the gases dissolved therein.

5 Claims, 7 Drawing Figures DE-GASSING or LIQUIDS loaded into an aircraft tank and taken to altitude (i.e., subjected to reduced pressure) two potential problems exist 1. the dissolved air may be suddenly released due to a stimulus such as an aircraft vibration or a sudden operation of a fuel pump. At an altitude of say 60,000 ft, the ambient pressure is such that the released air may represent some 210 percent of the fuel volume which, although the tank would be vented to atmosphere, can give'rise to a large transient pressure increase within the tank. This may result in tank damage or at least a loss of fuel from the tank due to fuel being forced out by, and/or entrained with, the excess air as it is vented to atmosphere. I

- 2. the dissolved air may be locally released within fuel pumps so that fuel is at least partly prevented from entering the pump impellor. The pump thus fails to function properly.

-An objectv of the present invention is to provide progressive removalof air dissolved within the fuel to preclude the onset of these two problems. i I

According to the invention a method of removing gases from a body of liquid, in which the gases have been dissolved at a first ambient pressure, comprises subjecting the liquid to a second ambient pressure of lower absolute value than the first ambient pressure, removing a proportion of the liquid from the body, causing the removed liquid to liberate at least some of the gases dissolved therein in the form of bubbles, and discharging the bubble-containing liquid into the remainder of the body in such a manner that the bubbles pass through the body, thereby releasing at least part of the gases dissolved therein.

Preferably the removed liquid is caused to liberate at least some of the gases dissolved therein in the form of bubbles at substantially the same time as that liquid is discharged into the remainder of the body of liquid. Preferably, also, the discharge is continuous over a period of time, throughout which bubbles are formed.

The proportion" of liquid removed from the body of liquid'is not a fixed proportion.

This invention is applicable to all liquids, but preferably the liquid is a fuel and preferably the dissolved gas is air. The equilibrium ratios of the volumes of air dissolved to volumes of bulk fuel vary for different fuels.

According to another aspect of the invention an aircraft fuel system comprises a tank, a vent associated with the tank and connected to atmosphere, at least one pump capable of delivering under pressure any fuel contained in the tank therefrom, and means for returning to the tank a proportion of such fuel that passes through the pump; the return means being such that, when the tank contains fuel and the'pump is in operation, the proportion of fuel passing through the return means is caused to liberate at least some of any air dissolved therein in the form of small bubbles and is discharged into the tank fuel.

It is found that, when the tank fuel is under a reduced ambient pressure, the passage of the cloud of small bubbles through the tank fuel acts to progressively release the majority of the air dissolved in the tank fuel. This result is thought to be due to the large surface area presented to the tank fuel by the cloud of small bubbles. Dissolved air is transferred from the tank fuel into the bubbles which, as gaseous pockets, enlarge as they pass through.the tank fuel to its surface. Air thus released from the bubbles is then vented to at-.

mosphere.

Considering an aircraft which has been refuelled at ground level, the air dissolved in that fuel is in a stable condition and cannot be removed by circulating fuel through the return means, i.e., the ratio of the mass of fers to a gaseous state in order to achieve the particular equilibrium ratio of mass of gas dissolved to mass ofliquid relating to that new second ambient pressure occurs naturally at any interface between the liquid and the gas. In aircraft fuel tanks, the surface area over which this process can naturally occur is insufficient to allow transfer at any useful rate. The present invention, however, enables the tank fuel to be progressively de-aerated, to an extent sufficient to preclude the onset of the two above-mentioned problems, in the time taken by the aircraft to reach its cruise altitude from take-off.

The invention is particularly useful because the air bubbles pass through the tank fuel are derived from air already dissolved'in the fuel. Thus, in effect, a proportion of the dissolved air is used to act as an agent for the release of most of the remaining air. The equipment system occupies little space, and there is special advantage in the fact that this extra equipment'has no 7 moving parts, and once fitted requires little attention.

One embodiment of the invention is illustrated diagrammatically by way of example in the accompanying drawings. ln these drawings:

FIG. 1 is a perspective view of part of an aircraft fuel system; I i

FIG. 1A is a fragmentary section taken along the line a'a of FIG. 1;

FIGS. 2A and 2B are enlarged detailed viewsof a component illustrated in FIG. 1, FIG. 213 being a section taken along the line 11-17 of HG. 2A; and,

FIGS. 3, 4 and 5 are plan view of three aircraft fuel tanks.

Referring initially to FIG. 1, an aircraft fuel tank 10, shown in broken outline, contains liquid fuel 10a. A typical fuel level for a nearly full tank is indicated at 10b. Above the fuel level, in the tank, is an air/fuel which are located near the bottom of the tank. As shown, the duct 14 has four branches l4c, each of FIGS.'2A and 2B show an orifice member 15. It is in the form of a hexagonally headed bolt, the shank 15a of which is adapted for flow connection with the duct 14. A bore 15d extends through the bolt co-axially with the shank as shown. Each flat portion 15b of the hexagon is formed with a radially directed orifice 15c extending into the bore 15d. An aperture 15e is provided co-axially with the bore 15d through the hexagonal head of the bolt.

Alternative orifice membersmay be provided. In an example, .not shown, the orifice member could comprisea series of small bore tubes extending radially from abla'nked-off end ofa duct 14.

The duct 14 (FIG. 1) extends upwards in the tank to a point 14a above the fuel-level 10b. The point 14a is located between the pump 12 and the orifice members and is provided with a small aperture 14b to break any siphon effectwhich would otherwise allow tank fuel to flow in reverse along the duct 14 and into the duct 13 during disconnection of the apparatus connected to the duct 13.

Alternatively a non-return valve (notshown) could be positioned in flow connection in the duct 14 which normally has a proportion of air dissolved in it.'

The pump 12 is operated either-continuously mat in tervals, depending on the requirements for fuel transfer or engine consumption during take-off and flight. During pump operation, pressurized fuel is fed initially along the duct 13 and some of this fuel enters the duct 14. This bleed fuel is expelled into the .tank fuel through the orifices 15c and apertures 15e. The apertures l5e act primarily, however, as'drain holes for any water which may have accumulated in the orifice members 15..

.The abrupt changes in velocity of the fuel passing through the orifices 15c cause at least some of the air dissolved therein to be liberated. It is also thought that shear forces in the fuel passing through the orifices help to release thedissolved air, which air passes upwards through the tank fuel in the form of a constant cloud of small bubbles 17. These small bubbles are found to cause a high proportion of the dissolved air in the tank fuel to be released. This released air passes to the fuel surface and is discharged to atmosphere through the vent 1 1.

The number and disposition of the orifice members 15 are not thought to be critical, provided that a large proportion of tank fuel is stimulated by the bubble clouds. The radially directed orifices cause the bubbles 17 to spray out laterally before rising.

It will be appreciated that aircraft fuel tanks are not necessarily regular in shape and FIGS. '3, 4 and 5 illustrate plan views of three fuel tanks of a delta winged aircraft, showing suitable positions for the orifice members 15. The maximum internal dimensions of the tanks shown in FIGS. 3, 4 and 5 are of the following orders of magnitude: 1

in FIG. 3, 13.0 m (510 inches);

in FIG. 4, 12.1 m (475 inches); and

in FIG. 5, 8.3 m (325 inches).

A suitable height for the orifice members above the tank floor is of the order of 50 to m/m (2 to 3 inches).

A suitable diameter for the duct 14 is 13 m/m (0.5 inch). Suitable diameters for the orifice 15c and the drain apertures 15e are 1.3 m/rn (0.05 inches). For these dimensions the pump 12, in addition to its normal function, should be capable of supplying 2 gallons of fuel per minute for each orifice member 15 at a pressure of approximately 25 pounds per square inch. It has been calculated that the de-aeration process is completed well within the time taken by the aircraft to reach its cruise altitude from take-off i.e., the time taken is in the order of minutes.

In the event of a tank having an installed pump which cannot be used in certain flight conditions, it is envisaged that a separate pump would be provided for deaeration purposes. In a tank having five orifice members 15 a suitable pump would be capable of-delivering 10 gallons of fuel per minute at a pressure of approxi mately 25 pounds per square inch.

The hole 14b, when provided, is preferably of 0.15 m/m diameter (0.06 inches).

We claim:

1. An apparatus for removing gases from liquid fuel in a tank, said gases being dissolved in said fuel at a first ambient pressure, said apparatus comprising:

a. vent means coupled tosaid tank for releasing said gases from said tank;

delivery duct means for carrying fuel from said tank;

at least one pump means for pumping said fuel from said tank into said delivery duct means;

return means for returning a portion of said fuel, pumped by said pump means, to said tank wherein said return means comprises means for permitting the liberation of a portion of the gases dissolved in said fuel, said liberated gasesbeing in the form of bubbles, and outlet means in said tank, below the level of said fuel, for dispersing said bubbles into the remaining fuel in said tank, when said fuel is at a second ambient pressure lower than said first ambient pressure, wherein said bubbles will flow to the top of said tank and will liberate said gases dislowering said ambient pressure to a second am bient pressure; removing a portion of said liquid from said tank; liberating said gases from said portion of said liquid, said liberated gases being in the form of bubbles in said liquid;

. passing said bubbles through the remainder of said liquid whereby the passage of said bubbles through said remainder of said liquid causes the'liberation of the gases dissolved in said remainder of said liquid. v 

2. The apparatus as set forth in claim 1 wherein said outlet means comprises a plurality of orifice means.
 3. The apparatus as set forth in claim 2 wherein said orifice means initially directs said bubbles in horizontal planes through said fuel.
 4. The apparatus as set forth in claim 1 wherein said gases consist of air.
 5. A method of removing gases from a liquid in a tank, said gases having been dissolved in said liquid at a first ambient pressure comprising: a. lowering said ambient pressure to a second ambient pressure; b. removing a portion of said liquid from said tank; c. liberating said gases from said portion of said liquid, said liberated gases being in the form of bubbles in said liquid; d. passing said bubbles through the remainder of said liquid whereby the passage of said bubbles through said remainder of said liquid causes the liberation of the gases dissolved in said remainder of said liquid. 